The present invention relates to a pneumatic tire with reduced road noise.
Road noise is a uncomfortable rumbling sound which may be heard inside of a vehicle when running on relatively rough road surfaces. Such rough road surfaces vibrate the tread portion of the tire, and this vibration is transmitted to the wheel rim, axis, suspension and body of the vehicle and then heard inside of the vehicle as road noise.
In general, as shown in FIG. 8, a pneumatic tire is provided in each bead portion with a bead core (a), and a carcass (b) is secured to the bead core (a) by wrapping the core therein. When the tire is mounted on a rim (j), the thin rubber layer (d) which exists between the carcass portion (b1) under the bead core (a) and the bead seat of the rim is compressed, and tensile strain acts on the carcass. Therefore, with respect to vibration, the tire is provided from the tread portion to the bead portion with a good channel for transmitting vibration.
In such a tire, it is very effective for reducing road noise to interfer with the transmission of vibration in the tread portion (where vibration is introduced), in other words at the boundary between the tire and road surface.
It has been therefore, proposed to use a soft tread rubber composition which is excellent at absorbing vibration and/or to increase the tread rubber thickness. However, in these methods, other running performances tend to deteriorate. For example, in the former method the wear resistance of the tread greatly decreases. In another method of obstructing vibration, it has been proposed to provide a rubber composition, which is excellent in vibration absorption, along the outer surface of the bead portion of the tire which which contacts with the rim flange. However, this method is insufficient for reducing the road noise effect. This method obstructs the transmission of vibration at the boundary between the tire and rim (the exit for the vibration). In this regard, this method is the same as the former method.